Mega slurry TBM ready for river crossing in China 17 Sep 2020

A 15m mega slurry TBM manufactured by CRCHI of China is ready for its role in construction of the twin tube Genshan East Road highway crossing under the Qiantang River in the city of Hangzhou near Shanghai in China. The TBM will excavate 3km of the total 4.7km long project that has about 2.3km at up to 44m beneath the river bed and a total length of 4.6km in tunnel to surface road connections either side. The twin tube tunnel will have three lanes in each tube and be designed for 80km/hr traffic speeds.

The project is to be built by the China Railway 14th Bureau. As is common practice for mega TBM projects in China, a different manufacturer will supply a TBM of similar dimension for the parallel TBM drive. The project is a total investment value of CYN 4.6 billion (USD$675 million).

15m mega slurry TBM ready for under-river highway drive

The 15m diameter mega CRCHI TBM has an installed power of about 9,755kW, a rated torque of 42,784 Nm, and the maximum excavation speed of 50mm/min.

The twin TBM drives are mainly through soft soils, including silty soil, mucky soil and cohesive soil. Construction difficulties will include:

• Maintaining stability of the mega 15m diameter face;
• Advancing through soft soil where poor bearing capacity stratum and poor permeability will cause the TBM to sink, and the segments to float, demanding high precision control of the TBM and high-quality segment ring build.
• Operating a large capacity slurry treatment plant;
• High reliability for TBM seals including the main bearing and main drive seals and tailskin seals;
• High wear resistance for the cutterhead, cutters, and slurry pipelines; and
• Constant monitoring of harmful gases expected to be encountered in the ground which will require a high-powered ventilation system on the TBM to discharge harmful gases when encountered.

The machine has been designed by the CRCHI research and development department to have:

• A soft soil cutterhead to feature cutter changes in free air;
• Frequency conversion motors for the main drive; and
• A retractable cutterhead.

Key highway project under Qiantang River in Hangzhou

The machine has been designed with additional technical features.

The rubber seals of the cutterhead main bearing will be automatically pressurized with a high precision gas system. There is no need for a person to adjust the pressure at the back of the rubber lip seals. The pressure on the rubber lip seals can be automatically set to balance the slurry pressure in the excavation chamber so as to protect the rubber lip seals from collapse due to high pressure in the excavation chamber. The high precision balance control ensures seal performance and reliability of the main drive seal and results in more precise control of the pressure in the excavation chamber to support the ground and avoid collapse of the tunnel face.

It is fitted also with two erectors to permit installation of the invert box culvert precast element simultaneously with erecting the segments of the segmental lining rings. The two erectors use the same traveler with the segment erector at the front and the box culvert erector at the back. Both are mechanical erectors with the segment erector lifting and installing the 10 segments per ring with seven standard segments, two neighbouring segments and a key in each ring.

Following successful factory testing, the TBM is ready to be shipped to site for assembly and a programmed launch in January of 2021. Breakthrough at the end of the 3.2km long drive is expected in March 2022. The double erector will eliminate a second pass to install the box culvert after excavation of the drive and will save time on the drive programme.